The present invention relates to a control valve for a refrigerating cycle which is to be applied to a variable capacity compressor. In particular, the present invention relates to a control valve for a variable capacity compressor, which is designed to control the supply of a cooling medium to be fed from a discharge pressure region to the crank chamber and the discharge of the cooling medium from the crank chamber to a suction region.
Since the compressor to be employed in the refrigerating cycle of the air conditioner for a vehicle is directly connected through a belt to the engine of vehicle, it is impossible to control the revolving speed of the compressor. Therefore, in order to realize an appropriate cooling capacity without being influenced by the revolving speed of the engine, variable capacity compressors which are capable of altering the compression capacity (discharge flow rate) thereof have been employed.
The variable capacity compressors are generally constructed such that the cooling medium which has been fed through a suction chamber communicated with an inlet duct is compressed before the cooling medium is discharged into a discharge chamber connected to a discharge duct, wherein the flow rate of the cooling medium to be discharged is altered depending on changes in pressure of the cooling medium in a pressure control chamber (crank chamber) which is designed to control the pressure of the cooling medium by means of a control valve. Japanese Patent Laid-open Publication (Kokai) 2002-303262, incorporated herein by reference, discloses a control valve for a refrigerating cycle, which is designed to control the cooling medium pressure in the crank chamber through the adjustment of opening and closing of the valve disposed on the inlet side, the adjustment being effected through the balance of cooling medium pressure between the cooling medium pressure of the variable capacity compressor and the reaction force of the bellows of the variable capacity compressor, thereby enabling the discharged cooling medium to flow from the discharge duct. It is thereby possible to adjust the cooling medium pressure in the crank chamber of the variable capacity compressors.
However, in order to realize a stable operation of the variable capacity compressor, it may occasionally be necessary to equalize the maximum flow rate upon the opening of the extraction valve. Further, in order to secure the minimum discharge flow rate of the variable capacity compressor, it may be necessary to secure a predetermined small flow rate upon the closing of the extraction valve.